Mice without the glands that make seminal fluid may sire sons with more body fat.

When sperm from male mice with no seminal fluid fertilized an egg, there were fewer viable sites for the embryo to implant itself in a female mouse's uterus, the placenta was heavier and the pregnancy rate was lower compared with eggs fertilized by sperm from healthy male mice. The male offspring of fathers lacking semen also had 72 percent more fat tissue 14 weeks after birth than sons of healthy male mice, researchers report January 27 in the Proceedings of the National Academy of Sciences.

The results suggest that levels of seminal fluid can influence the environment and development of embryos in mice, and the findings raise questions about the fluid’s role in human reproduction.